What is Seaweed? - Plant History
Welcome to Quatr.us Study Guides!

Seaweed

Seaweed
Seaweed

For the first two billion years of life on Earth, there were only one-celled creatures. But after early eukaryote cells began to reproduce by meiosis in addition to mitosis, about 1.4 billion years ago, they were able to evolve faster by mixing up their DNA with the DNA from other cells. They evolved in all kinds of ways, but a few of them evolved to stick to their sister cells after their parent divided, and these became the first creatures with more than one cell.

Beginning about 600 million years ago, seaweed was one of these early plants with more than one cell. Seaweed lived in the ocean. During the Proterozoic period, when seaweeds first evolved, the Earth was much colder than it is now. Most of the Earth's water was probably frozen into ice, and the oceans were shallower than they are now. Seaweed evolved to live in shallow ocean water, where there was enough sunlight for photosynthesis, and rocks to attach themselves to.

Because seaweed had more than one cell in the same plant, it needed a way to reproduce the whole plant and not just one cell at a time. Seaweeds reproduced themselves in two ways. Some seaweeds reproduced when a part of the plant broke off, maybe when a strong wave hit it or a rock fell on it. The small part of the plant could hold on to the rocks and grow into a new seaweed with the same DNA as the parent.

Kelp

Other seaweeds reproduced by using meiosis. Specialized patches on all the leaves produced haploid spores. These haploid spores then produced gametes, sperm and egg cells that could mix with other sperm and egg cells to make new diploid seaweed plants.

Seaweed also evolved other specialized cells that could help the whole plant survive. Different types of seaweed have different specialized cells. All seaweeds arrange their cells into flat leaves so that as many cells as possible get direct sunlight. Many seaweeds have holdfasts, finger-like projections like roots that hold on to the rocks. Some seaweeds have stalks that support the leaves like the stem of a flower. Some make hollow air-filled balls called floats, that hold the seaweed up closer to the surface of the water where there's more sunshine.

But seaweed has no vascular system to distribute food and water. Instead, each cell makes its own food by photosynthesis inside its chloroplasts. Because seaweed doesn't have a vascular system, scientists think of it as one of the algae instead of as a plant.

Learn by doing - Eating Seaweed
Next kind of plant - moss

Bibliography and further reading:

Plants
Animals
Biology
Chemistry
Math
Quatr.us home


LIMITED TIME OFFER FOR TEACHERS: Using this article with your class? Show us your class page where you're using this article, and we'll send you a free subscription so all your students can use Quatr.us Study Guides with no distractions! (Not a teacher? Paid subscriptions are also available for just $16/year!)
Please help other teachers and students find us: link to this page from your class page.
Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram or Twitter, or buy her book, Vandals to Visigoths.
Cite this page
  • Author: K.E. Carr
  • Title:
  • Site Name: Quatr.us Study Guides
  • Publisher: Quatr.us
  • Date Published:
Did you find what you needed? Ask your teacher to link to this page so other people can use it too! Send it in and win a Quatr.us "Great Page!" award!
Sign up for more free articles and special offers in Quatr.us' weekly newsletter:
We will never share your e-mail address unless you allow us to do so. View our privacy policy. Easy unsubscribe links are provided in every email.
Comment on This Article

Does your class page honor diversity, celebrate feminism, and support people of color, LBGTQ people, and people with disabilities? Let us know, and we'll send you a Diversity Banner you can proudly display!
Looking for more?
Quatr.us is loading comments...
(Comments will appear after moderation, if they are kind and helpful. Feel free to ask questions, and we'll try to answer them.)
Cite this page
  • Carr, K.E. . Quatr.us Study Guides, . Web. 28 April, 2017
ADVERTISEMENT